On Sat, 13 Jan 2007, dean gaudet wrote:

> ok here is the latest rev of this patch (against 2.6.20-rc4).
> 
> timings in cycles:
> 
>                 baseline   patched    baseline   patched
>                 no cache   no cache    cache      cache
> k8 pre-revF        21        16          14        17
> k8 revF            31        17          14        17
> core2              38        16          12        14
> p4                 49        41          24        24
> 
> the degredation in cached timings appears to be due to the 16 byte stack
> frame set up for the sidt instruction.  apparently due to -mno-red-zone...
> would you accept a patch which re-enables the red-zone for vsyscalls?

here is a first stab at a patch (applied on top of my vgetcpu sidt patch) 
which enables red-zone for vsyscall.  it fixes the cache degredation 
problem above by getting rid of the stack frame setup in vgetcpu (and 
improves the no cache cases as well but i haven't run it everywhere yet).

to do this i split the user-mode-only portion of vsyscall.c into 
vsyscall_user.c.  this required a couple externs in vsyscall.c and two 
extra ".globl" in the asm in vsyscall_user.c.

i'm not sure if we need the CFLAGS_vsyscall.o still or not.

let me know what you think... thanks.

-dean

Index: linux/arch/x86_64/kernel/Makefile
===================================================================
--- linux.orig/arch/x86_64/kernel/Makefile      2006-11-29 13:57:37.000000000 
-0800
+++ linux/arch/x86_64/kernel/Makefile   2007-01-13 23:34:22.000000000 -0800
@@ -6,7 +6,7 @@
 EXTRA_AFLAGS   := -traditional
 obj-y  := process.o signal.o entry.o traps.o irq.o \
                ptrace.o time.o ioport.o ldt.o setup.o i8259.o sys_x86_64.o \
-               x8664_ksyms.o i387.o syscall.o vsyscall.o \
+               x8664_ksyms.o i387.o syscall.o vsyscall.o vsyscall_user.o \
                setup64.o bootflag.o e820.o reboot.o quirks.o i8237.o \
                pci-dma.o pci-nommu.o alternative.o
 
@@ -45,6 +45,7 @@
 obj-y                          += intel_cacheinfo.o
 
 CFLAGS_vsyscall.o              := $(PROFILING) -g0
+CFLAGS_vsyscall_user.o         := $(PROFILING) -g0 -mred-zone
 
 therm_throt-y                   += ../../i386/kernel/cpu/mcheck/therm_throt.o
 bootflag-y                     += ../../i386/kernel/bootflag.o
Index: linux/arch/x86_64/kernel/vsyscall.c
===================================================================
--- linux.orig/arch/x86_64/kernel/vsyscall.c    2007-01-13 22:21:01.000000000 
-0800
+++ linux/arch/x86_64/kernel/vsyscall.c 2007-01-13 23:41:08.000000000 -0800
@@ -40,161 +40,12 @@
 #include <asm/segment.h>
 #include <asm/desc.h>
 #include <asm/topology.h>
-
-#define __vsyscall(nr) __attribute__ ((unused,__section__(".vsyscall_" #nr)))
-#define __syscall_clobber "r11","rcx","memory"
-
-int __sysctl_vsyscall __section_sysctl_vsyscall = 1;
-seqlock_t __xtime_lock __section_xtime_lock = SEQLOCK_UNLOCKED;
-
-/* is this necessary? */
-#ifndef CONFIG_NODES_SHIFT
-#define CONFIG_NODES_SHIFT 0
-#endif
-
 #include <asm/unistd.h>
 
-static __always_inline void timeval_normalize(struct timeval * tv)
-{
-       time_t __sec;
-
-       __sec = tv->tv_usec / 1000000;
-       if (__sec) {
-               tv->tv_usec %= 1000000;
-               tv->tv_sec += __sec;
-       }
-}
-
-static __always_inline void do_vgettimeofday(struct timeval * tv)
-{
-       long sequence, t;
-       unsigned long sec, usec;
-
-       do {
-               sequence = read_seqbegin(&__xtime_lock);
-               
-               sec = __xtime.tv_sec;
-               usec = __xtime.tv_nsec / 1000;
-
-               if (__vxtime.mode != VXTIME_HPET) {
-                       t = get_cycles_sync();
-                       if (t < __vxtime.last_tsc)
-                               t = __vxtime.last_tsc;
-                       usec += ((t - __vxtime.last_tsc) *
-                                __vxtime.tsc_quot) >> 32;
-                       /* See comment in x86_64 do_gettimeofday. */
-               } else {
-                       usec += ((readl((void __iomem *)
-                                  fix_to_virt(VSYSCALL_HPET) + 0xf0) -
-                                 __vxtime.last) * __vxtime.quot) >> 32;
-               }
-       } while (read_seqretry(&__xtime_lock, sequence));
-
-       tv->tv_sec = sec + usec / 1000000;
-       tv->tv_usec = usec % 1000000;
-}
-
-/* RED-PEN may want to readd seq locking, but then the variable should be 
write-once. */
-static __always_inline void do_get_tz(struct timezone * tz)
-{
-       *tz = __sys_tz;
-}
-
-static __always_inline int gettimeofday(struct timeval *tv, struct timezone 
*tz)
-{
-       int ret;
-       asm volatile("vsysc2: syscall"
-               : "=a" (ret)
-               : "0" (__NR_gettimeofday),"D" (tv),"S" (tz) : __syscall_clobber 
);
-       return ret;
-}
-
-static __always_inline long time_syscall(long *t)
-{
-       long secs;
-       asm volatile("vsysc1: syscall"
-               : "=a" (secs)
-               : "0" (__NR_time),"D" (t) : __syscall_clobber);
-       return secs;
-}
-
-int __vsyscall(0) vgettimeofday(struct timeval * tv, struct timezone * tz)
-{
-       if (!__sysctl_vsyscall)
-               return gettimeofday(tv,tz);
-       if (tv)
-               do_vgettimeofday(tv);
-       if (tz)
-               do_get_tz(tz);
-       return 0;
-}
-
-/* This will break when the xtime seconds get inaccurate, but that is
- * unlikely */
-time_t __vsyscall(1) vtime(time_t *t)
-{
-       if (!__sysctl_vsyscall)
-               return time_syscall(t);
-       else if (t)
-               *t = __xtime.tv_sec;            
-       return __xtime.tv_sec;
-}
-
-/* Fast way to get current CPU and node.
-   This helps to do per node and per CPU caches in user space.
-   The result is not guaranteed without CPU affinity, but usually
-   works out because the scheduler tries to keep a thread on the same
-   CPU.
-
-   tcache must point to a two element sized long array.
-   All arguments can be NULL. */
-long __vsyscall(2)
-vgetcpu(unsigned *cpu, unsigned *node, struct getcpu_cache *tcache)
-{
-       unsigned int p;
-       unsigned long j = 0;
-
-       /* Fast cache - only recompute value once per jiffies and avoid
-          relatively costly lsl/sidt otherwise.
-          This works because the scheduler usually keeps the process
-          on the same CPU and this syscall doesn't guarantee its
-          results anyways.
-          We do this here because otherwise user space would do it on
-          its own in a likely inferior way (no access to jiffies).
-          If you don't like it pass NULL. */
-       if (tcache && tcache->blob[0] == (j = __jiffies)) {
-               p = tcache->blob[1];
-       }
-       else {
-#ifdef VGETCPU_USE_SIDT
-                struct {
-                        char pad[6];   /* avoid unaligned stores */
-                        u16 size;
-                        u64 address;
-                } idt;
-
-                asm("sidt %0" : "=m" (idt.size));
-                p = idt.size - 0x1000;
-#else
-               /* Load per CPU data from GDT */
-               asm("lsl %1,%0" : "=r" (p) : "r" (__PER_CPU_SEG));
-#endif
-               if (tcache) {
-                       tcache->blob[0] = j;
-                       tcache->blob[1] = p;
-               }
-       }
-       if (cpu)
-               *cpu = p >> CONFIG_NODES_SHIFT;
-       if (node)
-               *node = p & ((1<<CONFIG_NODES_SHIFT) - 1);
-       return 0;
-}
-
-long __vsyscall(3) venosys_1(void)
-{
-       return -ENOSYS;
-}
+/* the vsyscalls themselves */
+extern int vgettimeofday(struct timeval * tv, struct timezone * tz);
+extern time_t vtime(time_t *t);
+extern long vgetcpu(unsigned *cpu, unsigned *node, struct getcpu_cache 
*tcache);
 
 #ifdef CONFIG_SYSCTL
 
@@ -259,6 +110,11 @@
 
 #endif
 
+/* is this necessary? */
+#ifndef CONFIG_NODES_SHIFT
+#define CONFIG_NODES_SHIFT 0
+#endif
+
 /* Assume __initcall executes before all user space. Hopefully kmod
    doesn't violate that. We'll find out if it does. */
 static void __cpuinit vsyscall_set_cpu(int cpu)
Index: linux/arch/x86_64/kernel/vsyscall_user.c
===================================================================
--- /dev/null   1970-01-01 00:00:00.000000000 +0000
+++ linux/arch/x86_64/kernel/vsyscall_user.c    2007-01-14 00:03:44.000000000 
-0800
@@ -0,0 +1,201 @@
+/*
+ *  linux/arch/x86_64/kernel/vsyscall_user.c
+ *
+ *  Copyright (C) 2001 Andrea Arcangeli <[EMAIL PROTECTED]> SuSE
+ *  Copyright 2003 Andi Kleen, SuSE Labs.
+ *
+ *  Thanks to [EMAIL PROTECTED] for some useful hint.
+ *  Special thanks to Ingo Molnar for his early experience with
+ *  a different vsyscall implementation for Linux/IA32 and for the name.
+ *
+ *  vsyscall 1 is located at -10Mbyte, vsyscall 2 is located
+ *  at virtual address -10Mbyte+1024bytes etc... There are at max 4
+ *  vsyscalls. One vsyscall can reserve more than 1 slot to avoid
+ *  jumping out of line if necessary. We cannot add more with this
+ *  mechanism because older kernels won't return -ENOSYS.
+ *  If we want more than four we need a vDSO.
+ *
+ *  Note: the concept clashes with user mode linux. If you use UML and
+ *  want per guest time just set the kernel.vsyscall64 sysctl to 0.
+ */
+
+#include <linux/time.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/timer.h>
+#include <linux/seqlock.h>
+#include <linux/jiffies.h>
+#include <linux/sysctl.h>
+#include <linux/getcpu.h>
+#include <linux/cpu.h>
+#include <linux/smp.h>
+#include <linux/notifier.h>
+
+#include <asm/vsyscall.h>
+#include <asm/pgtable.h>
+#include <asm/page.h>
+#include <asm/fixmap.h>
+#include <asm/errno.h>
+#include <asm/io.h>
+#include <asm/segment.h>
+#include <asm/desc.h>
+#include <asm/topology.h>
+
+#define __vsyscall(nr) __attribute__ ((unused,__section__(".vsyscall_" #nr)))
+#define __syscall_clobber "r11","rcx","memory"
+
+int __sysctl_vsyscall __section_sysctl_vsyscall = 1;
+seqlock_t __xtime_lock __section_xtime_lock = SEQLOCK_UNLOCKED;
+
+#include <asm/unistd.h>
+
+static __always_inline void timeval_normalize(struct timeval * tv)
+{
+       time_t __sec;
+
+       __sec = tv->tv_usec / 1000000;
+       if (__sec) {
+               tv->tv_usec %= 1000000;
+               tv->tv_sec += __sec;
+       }
+}
+
+static __always_inline void do_vgettimeofday(struct timeval * tv)
+{
+       long sequence, t;
+       unsigned long sec, usec;
+
+       do {
+               sequence = read_seqbegin(&__xtime_lock);
+
+               sec = __xtime.tv_sec;
+               usec = __xtime.tv_nsec / 1000;
+
+               if (__vxtime.mode != VXTIME_HPET) {
+                       t = get_cycles_sync();
+                       if (t < __vxtime.last_tsc)
+                               t = __vxtime.last_tsc;
+                       usec += ((t - __vxtime.last_tsc) *
+                                __vxtime.tsc_quot) >> 32;
+                       /* See comment in x86_64 do_gettimeofday. */
+               } else {
+                       usec += ((readl((void __iomem *)
+                                  fix_to_virt(VSYSCALL_HPET) + 0xf0) -
+                                 __vxtime.last) * __vxtime.quot) >> 32;
+               }
+       } while (read_seqretry(&__xtime_lock, sequence));
+
+       tv->tv_sec = sec + usec / 1000000;
+       tv->tv_usec = usec % 1000000;
+}
+
+/* RED-PEN may want to readd seq locking, but then the variable should be 
write-once. */
+static __always_inline void do_get_tz(struct timezone * tz)
+{
+       *tz = __sys_tz;
+}
+
+static __always_inline int gettimeofday(struct timeval *tv, struct timezone 
*tz)
+{
+       int ret;
+       asm volatile(
+                ".globl vsysc2\n"
+                "vsysc2: syscall\n"
+               : "=a" (ret)
+               : "0" (__NR_gettimeofday),"D" (tv),"S" (tz) : __syscall_clobber 
);
+       return ret;
+}
+
+static __always_inline long time_syscall(long *t)
+{
+       long secs;
+       asm volatile(
+                ".globl vsysc1\n"
+                "vsysc1: syscall\n"
+               : "=a" (secs)
+               : "0" (__NR_time),"D" (t) : __syscall_clobber);
+       return secs;
+}
+
+int __vsyscall(0) vgettimeofday(struct timeval * tv, struct timezone * tz)
+{
+       if (!__sysctl_vsyscall)
+               return gettimeofday(tv,tz);
+       if (tv)
+               do_vgettimeofday(tv);
+       if (tz)
+               do_get_tz(tz);
+       return 0;
+}
+
+/* This will break when the xtime seconds get inaccurate, but that is
+ * unlikely */
+time_t __vsyscall(1) vtime(time_t *t)
+{
+       if (!__sysctl_vsyscall)
+               return time_syscall(t);
+       else if (t)
+               *t = __xtime.tv_sec;
+       return __xtime.tv_sec;
+}
+
+/* is this necessary? */
+#ifndef CONFIG_NODES_SHIFT
+#define CONFIG_NODES_SHIFT 0
+#endif
+
+/* Fast way to get current CPU and node.
+   This helps to do per node and per CPU caches in user space.
+   The result is not guaranteed without CPU affinity, but usually
+   works out because the scheduler tries to keep a thread on the same
+   CPU.
+
+   tcache must point to a two element sized long array.
+   All arguments can be NULL. */
+long __vsyscall(2)
+vgetcpu(unsigned *cpu, unsigned *node, struct getcpu_cache *tcache)
+{
+       unsigned int p;
+       unsigned long j = 0;
+
+       /* Fast cache - only recompute value once per jiffies and avoid
+          relatively costly lsl/sidt otherwise.
+          This works because the scheduler usually keeps the process
+          on the same CPU and this syscall doesn't guarantee its
+          results anyways.
+          We do this here because otherwise user space would do it on
+          its own in a likely inferior way (no access to jiffies).
+          If you don't like it pass NULL. */
+       if (tcache && tcache->blob[0] == (j = __jiffies)) {
+               p = tcache->blob[1];
+       }
+       else {
+#ifdef VGETCPU_USE_SIDT
+                struct {
+                        char pad[6];   /* avoid unaligned stores */
+                        u16 size;
+                        u64 address;
+                } idt;
+
+                asm("sidt %0" : "=m" (idt.size));
+                p = idt.size - 0x1000;
+#else
+               /* Load per CPU data from GDT */
+               asm("lsl %1,%0" : "=r" (p) : "r" (__PER_CPU_SEG));
+#endif
+               if (tcache) {
+                       tcache->blob[0] = j;
+                       tcache->blob[1] = p;
+               }
+       }
+       if (cpu)
+               *cpu = p >> CONFIG_NODES_SHIFT;
+       if (node)
+               *node = p & ((1<<CONFIG_NODES_SHIFT) - 1);
+       return 0;
+}
+
+long __vsyscall(3) venosys_1(void)
+{
+       return -ENOSYS;
+}
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [EMAIL PROTECTED]
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Reply via email to